Fluoroscopic image density correction method, non-destructive inspection method, and image processing device

ABSTRACT

A reference density profile is generated in an outer circumference direction of a pipe having a reference welded portion on the basis of a reference fluoroscopic image generated from a radiation detection medium when a radiation source is disposed on a central axis of the pipe. A weld inspection density profile is generated in an outer circumference direction of a pipe having an inspection target welded portion on the basis of a weld inspection fluoroscopic image. On the basis of the reference density profile and the weld inspection density profile, density correction information is calculated. The density correction information is for correcting density irregularities in the weld inspection fluoroscopic image in the outer circumference direction of the pipe. On the basis of the density correction information, the density irregularities in the weld inspection fluoroscopic image are corrected.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2013/079965 filed on Nov. 6, 2013, which claims priority under 35U.S.C §119(a) to Patent Application No. 2012-255455 filed in Japan onNov. 21, 2012, all of which are hereby expressly incorporated byreference into the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluoroscopic image density correctionmethod, a non-destructive inspection method, and an image processingdevice capable of non-destructively inspecting for defects of weldedportions of pipes in a case of welding a plurality of pipes. Inparticular, the present invention relates to a fluoroscopic imagedensity correction method, a non-destructive inspection method, and animage processing device capable of obtaining the same inspection resultswithout dependency on the skill level of an inspector for identificationin images even if density irregularities occur in a fluoroscopic image.

2. Description of the Related Art

There is a known method of non-destructively inspecting for defects ofwelded portions of pipes in a case of welding a plurality of pipes. Forexample, non-destructive inspection is performed as follows. First,radiation, which originates from a radiation source and is transmittedthrough a welded portion of pipes, is detected by a sheet-like radiationdetection medium. A fluoroscopic image, which is generated by theradiation detection medium, is read from the radiation detection mediumby a dedicated scanner. The read fluoroscopic image is displayed on adisplay screen of a personal computer (hereinafter referred to as “PC”),and an inspector checks the image visually.

In the disclosure of JP2012-47569A, an external diameter point and aninner diameter point of a pipe are detected by using a luminance profilein a direction intersecting with the pipe in a radiation fluoroscopicimage of the pipe. In the disclosure of JP 1987-277542A(JP-S62-277542A), a thickness of a test pipe is calculated throughdensity comparison by performing radiographic imaging on a monitoringpipe of which a thickness is known and the test pipe of which thethickness is unknown at the same time.

In the disclosure of JP1986-274210A (JP-S61-274210A), whether sedimentsare present in a measurement target pipe is measured by comparing aradiation transmission measurement pattern, which is obtained byscanning the measurement target pipe, with a radiation transmissionmeasurement pattern which is obtained by scanning a reference pipe underthe same conditions.

In the disclosure of JP2005-037193A, in non-destructive inspection, aninspection target is placed on a rotational base which rotates withpredetermined angular displacement, and tomography is performed byradiation. In the inspection, an eccentricity of a central axis ofrotation of the inspection target is set as a parameter, and theeccentricity, which is obtained when a sharpness of a fluoroscopic image(cross-section image) is at the maximum, is specified as an optimumeccentricity of the central axis of rotation.

In the disclosure of JP2003-190125A, there is proposed image processingfor facilitating comparative reading of a plurality of medicalfluoroscopic images. A frequency distribution (histogram) of densityvalues (signal values) in a reference fluoroscopic image is calculated,the density value which has the maximum frequency in the frequencydistribution is calculated as a representative value, and imageprocessing (density correction) is performed on the other fluoroscopicimages such that the representative values of the other fluoroscopicimages are adjusted to the representative value of the referencefluoroscopic image (paragraphs 0049 to 0055).

SUMMARY OF THE INVENTION

In a fluoroscopic image of a welded portion of pipes, not only contrastsin density caused by defects (such as bubbles and cracks) of the weldedportion but also various density irregularities are exhibited. Forexample, distances from a radiation source are not uniform on aradiation detection medium, and thus density irregularities are caused.Further, since an amount of deviation (positioning error) from an idealposition of the radiation source is different for each inspection,density irregularities shown in the fluoroscopic image are different foreach inspection. That is, there is a following problem. In thefluoroscopic image of the welded portion of the pipes, not only variousdensity irregularities are exhibited, but also density irregularitiesdifferent for each inspection are exhibited. Thereby, identification ofdefects of the welded portion of the pipes greatly depends on anindividual identification skill of an inspector who performs visualinspection of the fluoroscopic image. Consequently, there are followingproblems. In order to prevent erroneous identification, a high-levelidentification skill is necessary for an inspector, and determinationresults may be different in accordance with a skill of an inspector.

In the disclosure of JP2012-47569A, the external diameter point and theinner diameter point of the pipe are detected by using the luminanceprofile in the direction intersecting with the pipe. However, in thedisclosure, there is no description regarding density correction of thefluoroscopic image based on the luminance profile.

In the disclosure of JP1987-277542A (JP-S62-277542A), the thickness ofthe test pipe is calculated through density comparison by performingradiographic imaging on the monitoring pipe of which the thickness isknown and the test pipe of which the thickness is unknown at the sametime. However, in the disclosure, there is no description regardingdensity correction of the fluoroscopic image based on the densityprofile. Further, in practice, it may be difficult to simultaneouslyperform radiographic imaging on a reference pipe and an inspectiontarget pipe at a field site in which the pipes are welded. In this case,even if the radiographic imaging is simultaneously performed, asdescribed above, there are various causes of density irregularities.Therefore, it is difficult to perfectly match the density irregularitiesshown in the fluoroscopic images on the basis of an image of thereference pipe and an image of the inspection target pipe.

In the disclosure of JP1986-274210A (JP-S61-274210A), scanning isperformed on the reference pipe and the measurement target pipe underthe same conditions. However, as described above, there are variouscauses of density irregularities. Thus, practically, it is difficult tocapture fluoroscopic images of the reference pipe and the measurementtarget pipe under perfectly the same conditions.

In the disclosure of JP2005-037193A, it is necessary to place theinspection target on the rotational base and capture a fluoroscopicimage thereof. Thus, it is difficult to apply the inspection method to acase of imaging the welded portion of the installed pipe. Further, thenumber and the time period of imaging operations using radiation arerestricted. Therefore, it is not realistic to perform imaging severaltimes while changing the imaging conditions.

In the disclosure of JP2003-190125A, there is proposed only a generaldensity adjustment technique. In the technique, in density correctionfor medical fluoroscopic images of a human body section, the frequencydistributions of density values of the fluoroscopic images arecalculated, and the density values of one fluoroscopic image, which havethe maximum frequencies, are adjusted to the density values of the otherfluoroscopic images which have the maximum frequencies. Consequently,practically, even if such a density adjustment technique is applied tofluoroscopic images of a welded portion of the pipes by simply adjustingthe density values in a specific region of one fluoroscopic image to thedensity values in a specific region of the other fluoroscopic images,typical density irregularities shown in the fluoroscopic image of thepipe are unlikely to be removed.

According to an aspect of the present invention, there is provided afluoroscopic image density correction method including: acquiring areference fluoroscopic image generated from a flexible radiationdetection medium, which is disposed on an outer circumference of areference pipe having a reference welded portion, in case where aradiation source is disposed on a central axis of the reference pipe andradiation originating from the radiation source is detected by theradiation detection medium; generating a reference density profile,which indicates a relationship between density values and coordinates onthe reference fluoroscopic image in a direction along the outercircumference of the reference pipe, on the basis of the referencefluoroscopic image; acquiring a weld inspection fluoroscopic imagegenerated from a flexible radiation detection medium, which is disposedon an outer circumference of an inspection target pipe, in case where aradiation source is disposed inside an inspection target pipe having aninspection target welded portion and radiation originating from theradiation source is detected by the radiation detection medium;generating a weld inspection density profile, which indicates arelationship between density values and coordinates on the weldinspection fluoroscopic image in a direction along the outercircumference of the inspection target pipe, on the basis of the weldinspection fluoroscopic image; calculating weld inspection densitycorrection information for correcting density irregularities in the weldinspection fluoroscopic image in the direction along the outercircumference of the inspection target pipe, on the basis of thereference density profile and the weld inspection density profile; andcorrecting the density irregularities in the weld inspectionfluoroscopic image in the direction along the outer circumference of theinspection target pipe, on the basis of the weld inspection densitycorrection information. With such a configuration, the reference densityprofile, which indicates a relationship between density values andcoordinates in the direction along the outer circumference of the pipe,is acquired on the basis of the reference fluoroscopic image which isobtained by performing radiographic imaging on the pipe having thereference welded portion, the weld inspection density profile, whichindicates a relationship between density values and coordinates in thedirection along the outer circumference of the pipe, is acquired on thebasis of the weld inspection fluoroscopic image which is obtained byperforming radiographic imaging on the pipe having the inspection targetwelded portion, and density irregularities in the direction along theouter circumference of the inspection target pipe are removed from theweld inspection fluoroscopic image through correction on the basis ofthe reference density profile and the weld inspection density profile.Therefore, it is possible to obtain the same inspection results withoutdependency on the skill level of an inspector for identification inimages even if density irregularities occur in the weld inspectionfluoroscopic image.

According to an aspect of the present invention, in the generating ofthe weld inspection density profile, a density profile of a weldedregion and a density profile of a non-welded region are generated, inwhich the welded region corresponds to the welded portion of theinspection target pipe in the weld inspection fluoroscopic image, andthe non-welded region corresponds to the non-welded portion of theinspection target pipe in the weld inspection fluoroscopic image, in thecalculating of the weld inspection density correction information,density correction information about the welded region of the weldinspection fluoroscopic image is calculated on the basis of the densityprofile of the welded region, and density correction information aboutthe non-welded region of the weld inspection fluoroscopic image iscalculated on the basis of the density profile of the non-welded region,and in the correcting of the weld inspection density, densityirregularities of the welded region are corrected on the basis of thedensity correction information about the welded region, and densityirregularities of the non-welded region are corrected on the basis ofthe density correction information about the non-welded region. Withsuch a configuration, even in case where density patterns of the weldedportion and the non-welded portion are different, density irregularitiesin the outer circumference direction are reliably removed from the weldinspection fluoroscopic image.

According to an aspect of the present invention, in the generating ofthe weld inspection density profile, the weld inspection density profileis generated by performing curve approximation on change in the densityvalue of the weld inspection fluoroscopic image in the direction alongthe outer circumference. With such a configuration, even in case wherevarious defects occur in the welded portion, it is possible to reliablyremove only density irregularities, and it is also possible to reliablyleave contrast of the defects.

According to an aspect of the present invention, the fluoroscopic imagedensity correction method further includes estimatingnear-radiation-source coordinates, which indicate a position on the weldinspection fluoroscopic image corresponding to a position closest to theradiation source on the radiation detection medium, on the basis of theweld inspection density profile, in which the near-radiation-sourcecoordinates are recorded in association with at least either one of theweld inspection fluoroscopic image in which the density irregularitiesare corrected or the weld inspection fluoroscopic image in which thedensity irregularities are not corrected. With such a configuration,even after density irregularities are removed from the weld inspectionfluoroscopic image, it is possible to check a position at which thedensity value is at the minimum due to positional deviation of theradiation source.

According to an aspect of the present invention, a diameter of theinspection target pipe is calculated on the basis of the weld inspectionfluoroscopic image or the weld inspection density profile, and thediameter of the inspection target pipe is recorded in association witheither one of the weld inspection fluoroscopic image in which thedensity irregularities are corrected or the weld inspection fluoroscopicimage in which the density irregularities are not corrected. With such aconfiguration, in case where there is an error in the diameter of theinspection target pipe, even though the diameter of the pipe is notactually measured, it is possible to detect an actual diameter of thepipe.

According to an aspect of the present invention, the weld inspectionfluoroscopic image, in which density irregularities are corrected, isdisplayed on a display screen, together with the reference fluoroscopicimage. Thereby, it is possible to easily identify whether or not thereare defects in the welded portion.

According to an aspect of the present invention, the weld inspectionfluoroscopic image, in which density irregularities are corrected, isdisplayed on the display screen, together with the weld inspectionfluoroscopic image in which density irregularities are not corrected.Thereby, it is possible to easily detect defects by visually checkingthe weld inspection fluoroscopic image obtained after the densityirregularity correction, and it is also possible to reliably checkwhether or not there are defects in the weld inspection fluoroscopicimage obtained before the density irregularity correction.

Further, according to an aspect of the present invention, there isprovided a fluoroscopic image density correction method including:acquiring a first inspection fluoroscopic image generated from aradiation detection medium, which is disposed to face a radiation sourcewith a welded portion of an inspection target pipe interposedtherebetween, at a first inspection; generating a first inspectiondensity profile, which indicates a relationship between a density valueand coordinates of the first inspection fluoroscopic image, on the basisof the first inspection fluoroscopic image; acquiring a secondinspection fluoroscopic image generated from a radiation detectionmedium, which is disposed to face a radiation source with the weldedportion of the inspection target pipe interposed therebetween, at asecond inspection; generating a second inspection density profile, whichindicates a relationship between a density value and coordinates of thesecond inspection fluoroscopic image, on the basis of the secondinspection fluoroscopic image; calculating inspection density correctioninformation for matching relationships between the density values andthe coordinates of the first inspection fluoroscopic image and thesecond inspection fluoroscopic image, on the basis of the firstinspection density profile and the second inspection density profile;and performing density correction for matching relationships between thedensity values and the coordinates of the first inspection fluoroscopicimage and the second inspection fluoroscopic image, on the basis of theinspection density correction information. With such a configuration,the first inspection density profile, which indicates a relationshipbetween the density values and the coordinates, is acquired on the basisof the first inspection fluoroscopic image which is obtained byperforming the first inspection (previous inspection), the secondinspection density profile, which indicates a relationship between thedensity values and the coordinates, is acquired on the basis of thesecond inspection fluoroscopic image which is obtained by performing thesecond inspection (current inspection), and density irregularities ofthe inspection target pipe are removed from the second inspectionfluoroscopic image (current inspection fluoroscopic image) on the basisof the first inspection density profile (the density profile of theprevious inspection) and the second inspection density profile (thedensity profile of the current inspection). Therefore, it is possible toreliably detect occurrence of defects without dependency on the skilllevel of an inspector for identification in images even if densityirregularities occur in the inspection fluoroscopic image.

According to an aspect of the present invention, in the generating ofthe first inspection density profile, the first inspection densityprofile is generated by performing curve approximation on change in thedensity value of the first inspection fluoroscopic image in a directionintersecting with the pipe, and in the generating of the secondinspection density profile, the second inspection density profile isgenerated by performing curve approximation on change in the densityvalue of the second inspection fluoroscopic image in a directionintersecting with the pipe. With such a configuration, even in casewhere various defects occur in the welded portion, it is possible toreliably remove only density irregularities, and it is also possible toreliably leave contrast of the defects.

According to an aspect of the present invention, the second inspectionfluoroscopic image, in which density is corrected by the fluoroscopicimage density correction method, is displayed on a display screen,together with the first inspection fluoroscopic image in which densityis corrected. Thereby, it is possible to reliably identify defects whichhave newly occurred in the welded portion.

According to an aspect of the present invention, the first inspectionfluoroscopic image and the second inspection fluoroscopic image, inwhich density is corrected by the fluoroscopic image density correctionmethod, are displayed on the display screen in a reduced manner on thebasis of the diameter of the calculated inspection target pipe. Withsuch a configuration, in case where there is an error in the diameter ofthe inspection target pipe, even though the diameter of the pipe is notactually measured, it is possible to increase or decrease the size ofthe inspection fluoroscopic image to an appropriate size.

According to an aspect of the present invention, the second inspectionfluoroscopic image, in which density is corrected, is displayed on thedisplay screen, together with the second inspection fluoroscopic imagein which density is not corrected.

Further, according to an aspect of the present invention, there isprovided an image processing device including: a fluoroscopic imageacquisition unit that acquires a reference fluoroscopic image generatedfrom a flexible radiation detection medium, which is disposed on anouter circumference of a reference pipe having a reference weldedportion, in case where a radiation source is disposed on a central axisof the reference pipe and radiation originating from the radiationsource is detected by the radiation detection medium, and a weldinspection fluoroscopic image generated from a flexible radiationdetection medium, which is disposed on an outer circumference of aninspection target pipe, in case where a radiation source is disposedinside an inspection target pipe having an inspection target weldedportion and radiation originating from the radiation source is detectedby the radiation detection medium at the time of weld inspection; adensity profile generation unit that generates a reference densityprofile, which indicates a relationship between a density value andcoordinates on the reference fluoroscopic image in a direction along theouter circumference of the reference pipe, on the basis of the referencefluoroscopic image, and generating a weld inspection density profile,which indicates a relationship between a density value and coordinateson the weld inspection fluoroscopic image in a direction along the outercircumference of the inspection target pipe, on the basis of the weldinspection fluoroscopic image; a density correction informationcalculation unit that calculates weld inspection density correctioninformation for correcting density irregularities in the weld inspectionfluoroscopic image in the direction along the outer circumference of theinspection target pipe, on the basis of the reference density profileand the weld inspection density profile; and a density correction unitthat corrects the density irregularities in the weld inspectionfluoroscopic image in the direction along the outer circumference of theinspection target pipe, on the basis of the weld inspection densitycorrection information.

Furthermore, according to an aspect of the present invention, there isprovided an image processing device including: a fluoroscopic imageacquisition unit that acquires an inspection fluoroscopic imagegenerated from a radiation detection medium which is disposed to face aradiation source with a welded portion of an inspection target pipeinterposed therebetween; a density profile generation unit thatgenerates an inspection density profile, which indicates a relationshipbetween a density value and coordinates of the inspection fluoroscopicimage, on the basis of the inspection fluoroscopic image; a densitycorrection information calculation unit that calculates inspectiondensity correction information for matching relationships between thedensity values and the coordinates of the inspection fluoroscopic imageobtained at a previous inspection and the inspection fluoroscopic imageobtained at a current inspection, on the basis of a first inspectiondensity profile generated from the inspection fluoroscopic imageobtained at the previous inspection and a second inspection densityprofile generated from the inspection fluoroscopic image obtained at thecurrent inspection; and a density correction unit that performs densitycorrection for matching relationships between the density values and thecoordinates of the inspection fluoroscopic image obtained at theprevious inspection and the inspection fluoroscopic image obtained atthe current inspection, on the basis of the inspection densitycorrection information.

According to the aspects of the present invention, it is possible toobtain the same inspection results without dependency on the skill levelof an inspector for identification in images even if densityirregularities occur in the fluoroscopic image of the welded portion ofthe pipes in case where inspection or measurement is performed using thefluoroscopic image of the welded portion of the pipes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are schematic diagrams illustrating situations ofcapture of fluoroscopic images during weld inspection.

FIG. 2 is a perspective view illustrating a positioning error of aradiation source.

FIG. 3 is a diagram illustrating a cross-section taken along the line3-3 of FIG. 2.

FIG. 4 is a cross-sectional view illustrating a state where theradiation source is disposed on the central axis of a welded portion ofpipes.

FIG. 5 is a diagram illustrating an example of a reference fluoroscopicimage which is obtained through radiographic imaging in the state ofFIG. 4.

FIG. 6 is a diagram illustrating a density profile of the referencefluoroscopic image of FIG. 5.

FIG. 7 is a cross-sectional view illustrating a state where theradiation source is disposed to be deviated from the central axis of thewelded portion of the pipes.

FIG. 8 is a diagram illustrating an example of a weld inspectionfluoroscopic image which is obtained through radiographic imaging in thestate of FIG. 7.

FIG. 9 is a diagram illustrating a density profile of the weldinspection fluoroscopic image of 85.

FIGS. 10A and 10B are diagrams illustrating an example of densityirregularity correction, where FIG. 10A is a weld inspectionfluoroscopic image obtained before the density irregularity correctionand FIG. 10B is a weld inspection fluoroscopic image obtained after thedensity irregularity correction.

FIG. 11 is a diagram illustrating a configuration example of an imageprocessing device.

FIG. 12 is a flowchart illustrating a flow to reference profilegeneration.

FIG. 13 is a flowchart illustrating a flow to density correction of theweld inspection fluoroscopic image.

FIG. 14 is a schematic diagram illustrating a situation of capture of afluoroscopic image during maintenance inspection.

FIG. 15 is an example of a density profile of a fluoroscopic imageduring the maintenance inspection.

FIG. 16 is a flowchart illustrating a flow of fluoroscopic imagecorrection processing during the maintenance inspection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, according to the accompanying drawings, embodiments of thepresent invention will be described.

Density Correction of Fluoroscopic Image During Weld Inspection

First, density correction and display of a fluoroscopic image duringweld inspection (inspection at the time of welding the pipe) will bedescribed.

Capture of Fluoroscopic Image and Positioning Error of Radiation SourceDuring Weld Inspection

FIGS. 1A, 1B, and 1C are schematic diagrams illustrating situations ofcapture of fluoroscopic images during weld inspection (hereinafterreferred to as “weld inspection fluoroscopic images”). FIG. 1A showspipes 10 which are not welded. FIG. 1B shows pipes 10 which are welded.FIG. 1C shows a pipe 10 in which a radiation source 20 emittingradiation and a radiation detection medium 30 detecting radiation aredisposed.

In FIGS. 1A to 1C, for convenience of description, forms of the pipes 10and weld forms of the pipes 10 are simplified. In practice, there arevarious forms of the pipes 10 and various weld forms of the pipes 10.The reference numeral 12 indicates a welded portion of the pipes 10. Inthe present description, the “welded portion” means a welded part of thepipes 10, and includes a weld material. The radiation source 20 isideally disposed on a central axis O of the pipe 10 as shown in FIG. 1C.The radiation detection medium 30 is flexible, and is wound around anouter circumference of the pipe 10 including the welded portion 12, asshown in FIG. 1C. As the radiation detection medium 30, in the presentexample, an imaging plate (stimulable phosphor film) is used. Theradiation originating from the radiation source 20 is transmittedthrough the welded portion 12 of the pipe 10 and a non-welded portion 14around the welded portion 12, and is detected by the radiation detectionmedium 30. The radiation detection medium 30 generates a weld inspectionfluoroscopic image having a density pattern corresponding to adistribution of radiation intensity on the radiation detection medium30.

Practically, in most cases, due to various situations of the field sitein which the pipes 10 are installed, the radiation source 20 may bedisposed at a position deviated from the central axis O of the pipe 10,as shown in the perspective view of FIG. 2 and the cross-sectional viewof FIG. 3 which shows a cross-section taken along the line 3-3 of FIG.2.

Errors (positioning errors) between an ideal position of the radiationsource 20 and a real position of the radiation source 20 are roughlyclassified into an error dx in a direction (length direction x) alongthe central axis O of FIG. 2 and errors dy and dz in the two directions(horizontal direction y, vertical direction z) which are orthogonal inthe cross-section of the pipe 10 of FIG. 3. When there are such errorsdx, dy, and dz, the intensity of the radiation on the radiationdetection medium 30 depends on a distance from the radiation source 20.Hence, density irregularities occur in a fluoroscopic image which isgenerated through the radiation detection medium 30.

Density Profile During Weld Inspection

As shown in FIG. 4, in case where the radiation source 20 is disposed atthe ideal position on the central axis O of the pipe 10, for example, afluoroscopic image 40 (hereinafter referred to as a “referencefluoroscopic image”) shown in FIG. 5 is acquired. The density profile(hereinafter referred to as a “reference density profile”) of areference fluoroscopic image 40 of FIG. 5 is shown in FIG. 6. Thereference density profile indicates a density pattern (a relationshipbetween the density values and the coordinates in an outer circumferencedirection c) of the reference fluoroscopic image 40 in the direction(outer circumference direction c) along the outer circumference of thepipe 10. In FIG. 4, for convenience of description, it is assumed thatradiation is uniformly and omnidirectionally emitted from the radiationsource 20, a thickness of the welded portion 12 of the pipe 10 isuniform along the outer circumference direction c, and there are nodefects in the welded portion 12.

In FIG. 4, the radiation source 20 is disposed at the ideal position onthe central axis O. Therefore, there are no positioning errors dx, dy,and dz of the radiation source 20 as shown in FIGS. 2 and 3(dx=dy=dz=0). That is, the distance from the radiation source 20 to theradiation detection medium 30 is uniformized along the outercircumference direction c. Accordingly, non-uniformity (radiationintensity unevenness) of the radiation intensity along the outercircumference direction c does not occur on the radiation detectionmedium 30.

In the reference fluoroscopic image 40 shown in FIG. 5, in a region 40 awhich corresponds to a portion (detection-effective portion 30 a) of theradiation detection medium 30 having no overlap, non-uniformity (densityirregularities) in density occurs in the outer circumference directionc. Here, if the thickness of the welded portion 12 is not uniform,change in density corresponding to a degree of non-uniformity occurs inthe image. In the reference fluoroscopic image 40 shown in FIG. 5, aregion, which is indicated by a reference numeral 40 b, is a regioncorresponding to a portion (detection-ineffective portion 30 b) of theradiation detection medium 30 having an overlap.

A weld inspection fluoroscopic image 42, which is obtained when theradiation source 20 is disposed to be deviated from the central axis Oas shown in FIG. 7, is shown in FIG. 8. Further, the density profile(hereinafter referred to as a “weld inspection density profile”) of theweld inspection fluoroscopic image 42 of FIG. 8 is shown in FIG. 9. Inaddition, for convenience of description, it is assumed that there is nopositioning error dx in a length direction x (dx=0). Furthermore, thereare no defects in the welded portion 12.

In FIG. 7, the radiation source 20 is disposed to be deviated from thecentral axis O. Therefore, the distance from the radiation source 20 tothe radiation detection medium 30 is not uniform along the outercircumference direction c. Accordingly, non-uniformity (radiationintensity unevenness) of the radiation intensity occurs on the radiationdetection medium 30. That is, even if the radiation originating from theradiation source 20 is uniformly and omnidirectionally emitted and thethickness of the welded portion 12 is uniform (constant) along the outercircumference direction c, density irregularities occur along the outercircumference direction c (horizontal direction of FIG. 8) in the weldinspection fluoroscopic image 42.

In case where defects of the welded portion 12 are detected by visuallychecking the weld inspection fluoroscopic image 42 shown in FIG. 8,density irregularities along the outer circumference direction c of thewelded portion 12 occur. Therefore, even in case where there are defectsin the welded portion 12, it is difficult to detect the defects.

Accordingly, in the embodiment of the present invention, densityirregularities are removed through image processing from the weldinspection fluoroscopic image 42 in which there are densityirregularities shown in FIG. 10A, and a weld inspection fluoroscopicimage 46, in which there are no density irregularities shown in FIG.10B, is output. Specifically, on the basis of the reference densityprofile shown in FIG. 6 and the weld inspection density profile shown inFIG. 9, density correction information for the weld inspectionfluoroscopic image 42 with density irregularities is calculated, anddensity irregularity correction is performed in accordance with thedensity correction information. Thereby, the weld inspectionfluoroscopic image 46 without density irregularities is generated.

In the weld inspection fluoroscopic image 42 shown in FIG. 8, a region,which is indicated by a reference numeral 42 b, is a regioncorresponding to a portion (detection-ineffective portion 30 b) of theradiation detection medium 30 having an overlap. Thus, the region is notshown in FIGS. 10A and 10B.

Image Processing Device Used in Weld Inspection

FIG. 11 is a block diagram illustrating a configuration example of animage processing device 50 used in a fluoroscopic image densitycorrection method according to the embodiment of the present invention.

The image processing device 50 of FIG. 11 includes: a scanner 51(fluoroscopic image acquisition unit), a storage section 52, a displaysection 53, an operation section 54, and a control section 55 (densityprofile generation unit, density correction information calculationunit, and density correction unit).

The scanner 51 acquires fluoroscopic images (a reference fluoroscopicimage and a weld inspection fluoroscopic image) from the radiationdetection medium 30.

The storage section 52 stores various kinds of information including thefluoroscopic images (the reference fluoroscopic image and the weldinspection fluoroscopic image) and the density profiles (the referencedensity profile and the weld inspection density profile). The storagesection 52 is constituted by a storage device such as a memory or adisk.

The display section 53 displays various kinds of information includingthe fluoroscopic images (the reference fluoroscopic image and the weldinspection fluoroscopic image) and the density profiles (the referencedensity profile and the weld inspection density profile). The displaysection 53 is constituted by a display device such as a liquid crystaldisplay device.

The operation section 54 receives various instruction inputs. Theoperation section 54 is constituted by an instruction input device suchas a keyboard or a touch panel.

The control section 55 is constituted by a microcomputer. The controlsection 55 performs various kinds of processing in accordance with aprogram which is stored in advance in the storage section 52.

The control section 55 has a function (density profile generationfunction) of generating the density profile (the reference densityprofile, the weld inspection density profile, and the like), as a firstfunction. The density profile indicates a relationship between thedensity values and the coordinates of the fluoroscopic images (thereference fluoroscopic image, the weld inspection fluoroscopic image,and the like) in a specific direction.

During the weld inspection, the control section 55 generates thereference density profile on the basis of the reference fluoroscopicimage which is generated by the radiation detection medium 30 in a statewhere the radiation source 20 is disposed on the central axis of thepipe 10. The reference density profile indicates at least a relationshipbetween the density values and the coordinates on the referencefluoroscopic image in the direction c along the outer circumference ofthe pipe 10. Further, the control section 55 generates the weldinspection density profile on the basis of the weld inspectionfluoroscopic image which is generated by the radiation detection medium30 in a state where the radiation source 20 is disposed at a positiondeviated from the central axis of the pipe 10. The weld inspectiondensity profile indicates at least a relationship between the densityvalues and the coordinates on the weld inspection fluoroscopic image inthe direction c along the outer circumference of the inspection targetpipe 10.

Further, the control section 55 has a function (density correctioninformation calculation function) of calculating density correctioninformation, as a second function, on the basis of two different densityprofiles. The density correction information is for correction thatmatches the relationships (density patterns) between the density valuesand the coordinates of one fluoroscopic image and another fluoroscopicimage in the specific direction.

During the weld inspection, the control section 55 calculates weldinspection density correction information, on the basis of the referencedensity profile and the weld inspection density profile. The informationis for correcting the density irregularities in the weld inspectionfluoroscopic image in the direction c along the outer circumference ofthe inspection target pipe 10. A specific example of the calculationwill be described later.

Furthermore, the control section 55 has a function (density irregularitycorrection function) of correcting density irregularities in thefluoroscopic image, as a third function, on the basis of the densitycorrection information. Here, correction of density irregularities meansremoval of density irregularities or reduction in densityirregularities.

During the weld inspection, the control section 55 corrects the densityirregularities in the weld inspection fluoroscopic image in thedirection c along the outer circumference of the inspection target pipe10, on the basis of the weld inspection density correction information.

In addition, the control section 55 has a function (fluoroscopic imagedisplay control function) of displaying the fluoroscopic image on thedisplay section 53, as a fourth function.

Density Profile Generation During Weld Inspection

The density profile indicates a correlation (density pattern) betweenthe density values and the coordinates of the fluoroscopic image in thespecific direction.

As the density irregularities shown in the weld inspection fluoroscopicimage, as described with reference to FIGS. 2 and 3, there are densityirregularities caused by the positioning errors dx, dy, and dz of theradiation source 20. In the weld inspection fluoroscopic image 42 shownin FIG. 8, particularly, due to errors dy and dz along the cross-sectionof the pipe 10 shown in FIG. 3, the density irregularities shown alongthe outer circumference direction c make it difficult to visualidentification as to whether or not there are defects in the weldedportion 12. Therefore, the control section 55 generates the weldinspection density profile by performing curve approximation on thechange in density values in the outer circumference direction c of theweld inspection fluoroscopic image 42. However, if it is determined thatstraight-line approximation is better than curve approximation,straight-line approximation may be performed. The curve approximationmay be performed using a well-known method. Further, by calculating anaverage value of the density values for each pixel group with apredetermined number of pixels along the outer circumference directionc, the density profile may be temporarily generated. Furthermore, thecross-section of the pipe 10 is circular, and the radiation detectionmedium 30 is wound around the circumference. That is, in case wherethere are positioning errors dx and dy, the distance from the radiationsource 20 to each position (coordinates) of the radiation detectionmedium 30 regularly changes along the outer circumference direction c.In accordance with the change, as density irregularities, the densityvalues regularly increase and decrease along the outer circumferencedirection c. Therefore, the curve approximation is performed usingregular change in density values along the outer circumferentialdirection c.

In the weld inspection fluoroscopic image, in case where there is adefect in the welded portion 12, a contrast is caused by the defect.However, by performing curve approximation, it is possible to obtain theweld inspection density profile which does not include the contrastcaused by the defect. That is, the control section 55 generates the weldinspection density profile which does not include the contrast caused bythe defect and appropriately indicates density irregularities.

Further, the control section 55 of the present example generates adensity profile of a welded region 42 d and a density profile of anon-welded region 42 c in the weld inspection fluoroscopic image 42.Here, the “welded region” is a region corresponding to the weldedportion 12 of the pipes 10 in the weld inspection fluoroscopic image 42.Further, the “non-welded region” is a region corresponding to thenon-welded portion 14 of the pipes 10 in the weld inspectionfluoroscopic image 42. For example, the respective density profiles aregenerated along a plurality of lines (only three lines 44 a, 44 b, and44 c are shown in FIG. 8) in the outer circumference direction c.

Likewise, the control section 55 of the present example generates thedensity profile of the welded region and the density profile of thenon-welded region in the reference fluoroscopic image 40 through curveapproximation or straight-line approximation.

Calculation of Density Correction Information During Weld Inspection

The control section 55 of the present example calculates a ratio ofdensity values (a ratio of the density value of the weld inspectiondensity profile to the density value of the reference density profile)at each set of the coordinates corresponding to each other in the outercircumference direction c on the basis of the reference density profileand the weld inspection density profile. Thereby, the control section 55calculates a correction coefficient (an inverse of the ratio of thedensity values) for each set of the coordinates along the outercircumference direction c in the weld inspection fluoroscopic image.

Further, the control section 55 generates the density correctioninformation about the welded region 42 d on the basis of the densityprofile of the welded region 42 d, and generates the density correctioninformation about the non-welded region 42 c on the basis of the densityprofile of the non-welded region 42 c.

The control section 55 of the present example performs the densitycorrection by multiplying the correction coefficient for each set of thecoordinates along the outer circumference direction c by the densityvalue of each pixel of the weld inspection fluoroscopic image.

Furthermore, the control section 55 of the present example correctsdensity irregularities in the welded region 42 d on the basis of thedensity correction information about the welded region 42 d, andcorrects density irregularities in the non-welded region 42 c on thebasis of the density correction information about the non-welded region42 c.

The contrasts caused by defects such as scratches and bubbles in thefluoroscopic image are easily recognizable in the fluoroscopic image dueto performing the density irregularity correction since change caused bythe density irregularities along the specific direction (outercircumference direction c) is localized compared with densityirregularities shown in the fluoroscopic image.

Estimation and Recording of Near-Radiation-Source Coordinates

The control section 55 of the present example calculates coordinates(near-radiation-source coordinates 43 of FIGS. 8 and 9), which indicatea position in the weld inspection fluoroscopic image 42, on the basis ofthe weld inspection density profile. The position corresponds to aposition closest to the radiation source 20 on the radiation detectionmedium 30.

In the horizontal axis direction (outer circumference direction c) ofthe weld inspection fluoroscopic image 42 shown in FIG. 8, thecoordinates at which the density is highest is the near-radiation-sourcecoordinates. That is, in the horizontal axis direction (outercircumference direction c) of the weld inspection density profile shownin FIG. 9, the coordinates at which the density value is the maximumvalue is the near-radiation-source coordinates. As shown in FIG. 8, thecontrol section 55 generates the respective density profiles along theplurality of lines (only three lines 44 a, 44 b, and 44 c are shown inFIG. 8) in the outer circumference direction c, calculates thecoordinates (maximum value coordinates) with maximum value for eachdensity profile, and estimates the near-radiation-source coordinates 43on the basis of the plurality of maximum value coordinates.

Further, the control section 55 records the estimatednear-radiation-source coordinates in the storage section 52 inassociation with the weld inspection fluoroscopic image (at least onefluoroscopic image of the weld inspection fluoroscopic image in whichdensity irregularities are corrected and the weld inspectionfluoroscopic image in which density irregularities are not corrected).

Calculation and Recording of Pipe Diameter

The control section 55 of the present example calculates an outerdiameter (radius) of the pipe 10 on the basis of the weld inspectionfluoroscopic image or the weld inspection density profile. Further, thecontrol section 55 records attribute information including the outerdiameter r in the storage section 52 in association with the weldinspection fluoroscopic image (at least one fluoroscopic image of theweld inspection fluoroscopic image in which density irregularities arecorrected and the weld inspection fluoroscopic image in which densityirregularities are not corrected).

In case where the outer diameter (radius) of the pipe 10 is set as r, alength L of the portion (detection-effective portion 30 a) of theradiation detection medium 30 having no overlap corresponds to the outercircumference of the pipe 10 of 2πr (L=2πr). Accordingly, the controlsection 55 detects coordinates of an edge 45 (a point at which thedensity value is suddenly lowered) of the density from the weldinspection density profile, calculates the length L of thedetection-effective portion 30 a of the radiation detection medium 30corresponding to the coordinates of the edge 45 on the basis of thecoordinates of the edge 45 and a resolution of the weld inspectionfluoroscopic image, and calculates the outer diameter r (=L/2π) of thepipe 10 on the basis of the length L.

Example of Density Correction Processing During Weld Inspection

Next, a flow of an example of density correction processing of thefluoroscopic image during the weld inspection will be described.

FIG. 12 is a flowchart illustrating a flow from the referencefluoroscopic image acquisition to the reference profile storage.

First, the reference fluoroscopic image is acquired (step S2). Forexample, as shown in FIG. 1C, the radiation source 20 is disposed on thecentral axis O of the reference pipe 10, and the flexible radiationdetection medium 30 is wound around the outer circumference of thewelded portion 12 of the reference pipe 10. The radiation, whichoriginates from the radiation source 20 during a constant time periodand is transmitted through the welded portion 12 of the pipe 10, isdetected through the radiation detection medium 30. The referencefluoroscopic image is generated through the radiation detection medium30. Thus, the radiation detection medium 30 is removed from the weldedportion 12 of the pipe 10, and a dedicated scanner 51 reads thereference fluoroscopic image from the radiation detection medium 30.Thereby, the reference fluoroscopic image 40 shown in FIG. 5 isacquired, and is stored in the storage section 52.

It should be noted that, in case where a reference fluoroscopic image isstored in the storage section 52 in advance, the reference fluoroscopicimage may be acquired from the storage section 52.

Next, on the basis of the reference fluoroscopic image, the referencedensity profile shown in FIG. 6 is generated (step S4). The referencedensity profile indicates the relationship between the density valuesand the coordinates (density pattern) of the reference fluoroscopicimage in the direction c along the outer circumference of the weldedportion 12 of the reference pipe 10.

Next, the reference density profile is stored in the storage section 52in association with the reference fluoroscopic image 40 (step S6).

FIG. 13 is a flowchart illustrating a flow from the weld inspectionfluoroscopic image acquisition to the density correction of the weldinspection fluoroscopic image.

After a welding operation between the pipe 10 and the pipe 10 at theweld field site is performed, the weld inspection fluoroscopic image isacquired (step S12). For example, as shown in FIG. 7, the radiationsource 20 is disposed inside the welded portion 12 of the inspectiontarget pipe 10, and the flexible radiation detection medium 30 is woundaround the outer circumference of the welded portion 12 of theinspection target pipe 10. The radiation, which originates from theradiation source 20 during a constant time period and is transmittedthrough the welded portion 12 of the pipe 10, is detected through theradiation detection medium 30. The weld inspection fluoroscopic image isgenerated through the radiation detection medium 30. Then, the radiationdetection medium 30 is removed from the welded portion 12 of the pipe10, and a dedicated scanner 51 reads the weld inspection fluoroscopicimage from the radiation detection medium 30. Thereby, the weldinspection fluoroscopic image 42 shown in FIG. 8 is acquired.

It should be noted that, in case where a weld inspection fluoroscopicimage is stored in the storage section 52 in advance, the weldinspection fluoroscopic image may be acquired from the storage section52.

Next, on the basis of the weld inspection fluoroscopic image, the weldinspection density profile shown in FIG. 9 is generated (step S14). Theweld inspection density profile indicates the relationship between thedensity values and the coordinates (density pattern) of the weldinspection fluoroscopic image in the direction c along the outercircumference of the welded portion 12 of the inspection target pipe 10.

Next, on the basis of the reference density profile and the weldinspection density profile, weld inspection density correctioninformation is calculated (step S16). The information is for correctingdensity irregularities in the weld inspection fluoroscopic image in thedirection c along the outer circumference of the inspection target pipe10.

Next, on the basis of the weld inspection density profile, attributeinformation is calculated (step S18). In the present example, the outerdiameter r (radius) of the inspection target pipe 10 and thenear-radiation-source coordinates 43 are calculated.

Next, on the basis of the weld inspection density correctioninformation, the density irregularities in the weld inspectionfluoroscopic image in the direction c along the outer circumference ofthe welded portion 12 of the pipe 10 are corrected (step S20).

Next, the reference fluoroscopic image and the weld inspectionfluoroscopic image, in which density irregularities are corrected, aredisplayed on the display section 53 (step S22).

Display of Fluoroscopic Image During Weld Inspection

The control section 55 of the present example causes a screen (displayscreen) of the display section 53 to display both the weld inspectionfluoroscopic image, in which density irregularities are corrected, andthe reference fluoroscopic image.

Further, the control section 55 of the present example causes the screen(display screen) of the display section 53 to display both the weldinspection fluoroscopic image, in which density irregularities arecorrected, and the weld inspection fluoroscopic image, in which densityirregularities are not corrected, in response to an instruction inputfrom the operation section 54.

Density Correction of Fluoroscopic Image During Maintenance Inspection

Next, density correction and display of a fluoroscopic image duringmaintenance inspection (inspection at the time of pipe maintenance) willbe described.

Capture of Fluoroscopic Image and Positioning Error of Radiation SourceDuring Maintenance Inspection

FIG. 14 is a schematic diagram illustrating a situation of capture of afluoroscopic image during maintenance inspection (hereinafter referredto as a “maintenance inspection fluoroscopic image”). As shown in FIG.14, during the maintenance inspection, the radiation source 20 and theradiation detection medium 30 are disposed to face each other with thewelded portion 12 of the inspection target pipe 10 interposedtherebetween. The radiation emitted from the radiation source 20 istransmitted through the welded portion 12 of the pipe 10 and anon-welded portion 14 around the welded portion 12, and is detected bythe radiation detection medium 30. The radiation detection medium 30generates a maintenance inspection fluoroscopic image corresponding to adistribution of radiation intensity on the radiation detection medium30.

Errors (positioning errors) between the ideal position of the radiationsource 20 and the real position of the radiation source 20 are roughlyclassified into an error in the x direction (the length direction of thepipe 10) of FIG. 14, an error in the y direction (the direction of thedistance from the radiation source 20 to the pipe 10) of FIG. 14, and anerror in the z direction (the direction intersecting with the pipe 10)of FIG. 14. In case where such an error occurs, density irregularitiesoccur in the fluoroscopic image which is generated through the radiationdetection medium 30.

Density Profile During Maintenance Inspection

FIG. 15 shows an example of a density profile (hereinafter referred toas a “maintenance inspection density profile”). The density profile isgenerated by the control section 55 of the image processing device 50,on the basis of the maintenance inspection fluoroscopic image acquiredfrom the radiation detection medium 30. The maintenance inspectiondensity profile indicates a density pattern (a relationship between thedensity values and the z coordinates) in the direction z intersectingwith the pipe 10.

Image Processing Device

By using the image processing device 50 shown in FIG. 11, it is possibleto perform density irregularity correction of the maintenance inspectionfluoroscopic image.

The scanner 51 acquires the maintenance inspection fluoroscopic imagefrom the radiation detection medium 30. The storage section 52 storesvarious kinds of information including the maintenance inspectionfluoroscopic image and the maintenance inspection density profile. Thedisplay section 53 displays various kinds of information including themaintenance inspection fluoroscopic image and the maintenance inspectiondensity profile. In a manner similar to that of the above-mentioned weldinspection, the control section 55 executes various kinds of processing,in accordance with programs which are stored in the storage section 52in advance. The control section 55 has a density profile generationfunction, a density correction information calculation function, adensity irregularity correction function, a fluoroscopic image displaycontrol function, and the like.

During the maintenance inspection, the control section 55 generates themaintenance inspection density profile on the basis of the maintenanceinspection fluoroscopic image. The maintenance inspection densityprofile indicates a relationship between the density values and thecoordinates of the maintenance inspection fluoroscopic image in aspecific direction. Further, during the maintenance inspection, thecontrol section 55 calculates correction information (inspection densitycorrection information) on the basis of the maintenance inspectiondensity profile (first inspection density profile) at the previousmaintenance inspection and the maintenance inspection density profile(second inspection density profile) at the current maintenanceinspection. The correction information is for matching relationshipsbetween the density values and the coordinates of the previousmaintenance inspection fluoroscopic image (first inspection fluoroscopicimage) and the current maintenance inspection fluoroscopic image (secondinspection fluoroscopic image) in the specific direction. Furthermore,during the maintenance inspection, the control section 55 performs thedensity irregularity correction, on the basis of the inspection densitycorrection information. The correction is for matching relationshipsbetween the density values and the coordinates of the previousmaintenance inspection fluoroscopic image and the current maintenanceinspection fluoroscopic image in the specific direction.

Specific Example of Density Profile Generation

During the maintenance inspection, the radiation source 20 and theradiation detection medium 30 are disposed to face each other with thewelded portion 12 of the inspection target pipe 10 interposedtherebetween. In the present example, in the maintenance inspectionfluoroscopic image, the horizontal direction corresponds to the xdirection (the length direction of the pipe 10) of FIG. 14, and thevertical direction corresponds to the z direction of FIG. 14. In themaintenance inspection density profile shown in FIG. 15, the horizontaldirection indicates the coordinates in the direction (the z direction ofFIG. 14) intersecting with the pipe 10, and the vertical directionindicates the density values.

The density irregularities include density irregularities which appearalong the horizontal direction (corresponding to the length direction ofthe pipe 10) of the maintenance inspection fluoroscopic image since theradiation source 20 is deviated from a target position (the center ofthe welded portion 12, for example, the contact point between the pipe10 and the pipe 10) in the length direction (the x direction of FIG. 14)of the pipe 10. Further, the density irregularities include densityirregularities which appear along the vertical direction (correspondingto the direction y intersecting with the pipe 10) of the maintenanceinspection fluoroscopic image since the radiation source 20 is deviatedfrom a target position in the direction (the y direction of FIG. 14)from the radiation source 20 toward the pipe 10. Furthermore, thedensity irregularities include density irregularities which appear alongthe vertical direction (corresponding to the z direction) of themaintenance inspection fluoroscopic image since the radiation source 20is deviated from a target position in the z direction of FIG. 14.

The control section 55 of the present example generates the maintenanceinspection density profile of the maintenance inspection fluoroscopicimage. The profile indicates a density pattern (a relationship betweenthe density values and the coordinates of the maintenance inspectionfluoroscopic image) of the maintenance inspection fluoroscopic image inthe specific direction.

Specific Example of Calculation of Density Correction Information

The control section 55 of the present example generates the maintenanceinspection density profile shown in FIG. 15 by performing curveapproximation on the change in density values in the direction (the zdirection of FIG. 14) intersecting with the pipe of the maintenanceinspection fluoroscopic image.

Display of Fluoroscopic Image During Maintenance Inspection

The control section 55 of the present example causes the screen (displayscreen) of the display section 53 to display both the fluoroscopic image(the second inspection fluoroscopic image obtained after the densitycorrection), in which density irregularities are corrected, at thecurrent maintenance inspection and the fluoroscopic image (the firstinspection fluoroscopic image obtained after the correction), in whichdensity irregularities are corrected, at the previous maintenanceinspection.

Further, the control section 55 of the present example causes the screen(display screen) of the display section 53 to display both the currentmaintenance inspection fluoroscopic image (the second inspectionfluoroscopic image obtained after the density correction), in whichdensity is corrected, and the current maintenance inspectionfluoroscopic image (the second inspection fluoroscopic image obtainedbefore the density correction), in which density is not corrected, inresponse to an instruction input from the operation section 54.

Enlargement or Reduction of Fluoroscopic Image During MaintenanceInspection

The control section 55 of the present example enlarges or reduces thefluoroscopic image (the second inspection fluoroscopic image obtainedafter the density correction), in which density irregularities arecorrected, at the current maintenance inspection and the fluoroscopicimage (the first inspection fluoroscopic image obtained after thedensity correction), in which the density irregularities are corrected,at the previous maintenance inspection, on the basis of the diameter ofthe pipe calculated during the weld inspection, and causes the screen(display screen) of the display section 53 to display the fluoroscopicimages.

Example of Fluoroscopic Image Correction Processing During MaintenanceInspection

Referring to the flowchart of FIG. 16, an example of fluoroscopic imagecorrection processing during the maintenance inspection will bedescribed.

First, the maintenance inspection fluoroscopic image is acquired (stepS42). In the present example, as described in FIG. 14, the radiationsource 20 and the sheet-like radiation detection medium 30 are disposedto face each other with the welded portion 12 of the inspection targetpipe 10 interposed therebetween. Radiation is emitted from the radiationsource 20 during a constant time period, and the radiation transmittedthrough the welded portion 12 of the pipe 10 is detected through theradiation detection medium 30 which is disposed to face the radiationsource 20. Thereby, the maintenance inspection fluoroscopic image isgenerated through the radiation detection medium 30. The dedicatedscanner 51 reads the maintenance inspection fluoroscopic image from theradiation detection medium 30, thereby acquiring the maintenanceinspection fluoroscopic image, and the image is stored in the storagesection 52.

Next, on the basis of the maintenance inspection fluoroscopic image, themaintenance inspection density profile shown in FIG. 15 is generated(step S44). The maintenance inspection density profile indicates adensity pattern (a relationship between the density values and thecoordinates) of the maintenance inspection fluoroscopic image in thespecific direction (the z direction in the present example).

Next, the maintenance inspection fluoroscopic image and the maintenanceinspection density profile are associated with each other and arerecorded in the storage section 52 (step S46).

It is determined whether or not the fluoroscopic image at the previousmaintenance inspection is present in the storage section 52 (step S48).If there is no fluoroscopic image, prescribed density correction isperformed (step S50). That is, in a case of the first maintenanceinspection, there is no fluoroscopic image at the previous maintenanceinspection, and thus the density irregularity correction is performed onthe basis of the fluoroscopic image at the current maintenanceinspection.

In the second and following maintenance inspections, the currentmaintenance inspection fluoroscopic image is acquired in step S42, thecurrent maintenance inspection density profile is generated in step S44,the maintenance inspection density profile is associated with thecurrent maintenance inspection fluoroscopic image, and is recorded inthe storage section 52, and a previous (first) maintenance inspectionfluoroscopic image is present in the storage section 52. Therefore,processing of steps S52 to S56 is performed.

If the previous maintenance inspection fluoroscopic image is present inthe storage section 52, the control section 55 calculates themaintenance inspection density correction information on the basis ofthe previous maintenance inspection density profile (first inspectiondensity profile) and the current maintenance inspection density profile(second inspection density profile) (step S52). The information is formatching density patterns (relationships between the density values andthe coordinates) of the current maintenance inspection fluoroscopicimage and the previous maintenance inspection fluoroscopic image in thespecific direction (the z direction in the present example).

Next, on the basis of the maintenance inspection density correctioninformation, the density correction of the current maintenanceinspection fluoroscopic image is performed (step S54).

Next, the current maintenance inspection fluoroscopic image obtainedafter the correction is displayed on the screen of the display section53 (step S56).

It should be noted that the present invention is not limited to theexamples described in the present specification and the examples shownin the drawings. It is apparent that various design changes andmodifications may be performed without departing from the scope of thepresent invention.

What is claimed is:
 1. A fluoroscopic image density correction methodcomprising: acquiring a reference fluoroscopic image generated from aflexible radiation detection medium, which is disposed on an outercircumference of a reference pipe having a reference welded portion, incase where a radiation source is disposed on a central axis of thereference pipe and radiation originating from the radiation source isdetected by the radiation detection medium; generating a referencedensity profile, which indicates a relationship between density valuesand coordinates on the reference fluoroscopic image in a direction alongthe outer circumference of the reference pipe, on the basis of thereference fluoroscopic image; acquiring a weld inspection fluoroscopicimage generated from a flexible radiation detection medium, which isdisposed on an outer circumference of an inspection target pipe, in casewhere a radiation source is disposed inside an inspection target pipehaving an inspection target welded portion and radiation originatingfrom the radiation source is detected by the radiation detection medium;generating a weld inspection density profile, which indicates arelationship between density values and coordinates on the weldinspection fluoroscopic image in a direction along the outercircumference of the inspection target pipe, on the basis of the weldinspection fluoroscopic image; calculating weld inspection densitycorrection information for correcting density irregularities in the weldinspection fluoroscopic image in the direction along the outercircumference of the inspection target pipe, on the basis of thereference density profile and the weld inspection density profile; andcorrecting the density irregularities in the weld inspectionfluoroscopic image in the direction along the outer circumference of theinspection target pipe, on the basis of the weld inspection densitycorrection information.
 2. The fluoroscopic image density correctionmethod according to claim 1, wherein in the generating of the weldinspection density profile, a density profile of a welded region and adensity profile of a non-welded region are generated, in which thewelded region corresponds to the welded portion of the inspection targetpipe in the weld inspection fluoroscopic image, and the non-weldedregion corresponds to the non-welded portion of the inspection targetpipe in the weld inspection fluoroscopic image, wherein in thecalculating of the weld inspection density correction information,density correction information about the welded region of the weldinspection fluoroscopic image is calculated on the basis of the densityprofile of the welded region, and density correction information aboutthe non-welded region of the weld inspection fluoroscopic image iscalculated on the basis of the density profile of the non-welded region,and wherein in the correcting of the weld inspection density, densityirregularities of the welded region are corrected on the basis of thedensity correction information about the welded region, and densityirregularities of the non-welded region are corrected on the basis ofthe density correction information about the non-welded region.
 3. Thefluoroscopic image density correction method according to claim 1,wherein in the generating of the weld inspection density profile, theweld inspection density profile is generated by performing curveapproximation on change in the density value of the weld inspectionfluoroscopic image in the direction along the outer circumference. 4.The fluoroscopic image density correction method according to claim 2,wherein in the generating of the weld inspection density profile, theweld inspection density profile is generated by performing curveapproximation on change in the density value of the weld inspectionfluoroscopic image in the direction along the outer circumference. 5.The fluoroscopic image density correction method according to claim 1,further comprising estimating near-radiation-source coordinates, whichindicate a position on the weld inspection fluoroscopic imagecorresponding to a position closest to the radiation source on theradiation detection medium, on the basis of the weld inspection densityprofile, wherein the near-radiation-source coordinates are recorded inassociation with at least either one of the weld inspection fluoroscopicimage in which the density irregularities are corrected or the weldinspection fluoroscopic image in which the density irregularities arenot corrected.
 6. The fluoroscopic image density correction methodaccording to claim 2, further comprising estimatingnear-radiation-source coordinates, which indicate a position on the weldinspection fluoroscopic image corresponding to a position closest to theradiation source on the radiation detection medium, on the basis of theweld inspection density profile, wherein the near-radiation-sourcecoordinates are recorded in association with at least either one of theweld inspection fluoroscopic image in which the density irregularitiesare corrected or the weld inspection fluoroscopic image in which thedensity irregularities are not corrected.
 7. The fluoroscopic imagedensity correction method according to claim 1, wherein a diameter ofthe inspection target pipe is calculated on the basis of the weldinspection fluoroscopic image or the weld inspection density profile,and the diameter of the inspection target pipe is recorded inassociation with either one of the weld inspection fluoroscopic image inwhich the density irregularities are corrected or the weld inspectionfluoroscopic image in which the density irregularities are notcorrected.
 8. The fluoroscopic image density correction method accordingto claim 2, wherein a diameter of the inspection target pipe iscalculated on the basis of the weld inspection fluoroscopic image or theweld inspection density profile, and the diameter of the inspectiontarget pipe is recorded in association with either one of the weldinspection fluoroscopic image in which the density irregularities arecorrected or the weld inspection fluoroscopic image in which the densityirregularities are not corrected.
 9. A non-destructive inspectionmethod, wherein the weld inspection fluoroscopic image, in which densityirregularities are corrected by the fluoroscopic image densitycorrection method according to claim 1, is displayed on a displayscreen, together with the reference fluoroscopic image.
 10. Anon-destructive inspection method, wherein the weld inspectionfluoroscopic image, in which density irregularities are corrected by thefluoroscopic image density correction method according to claim 2, isdisplayed on a display screen, together with the reference fluoroscopicimage.
 11. The non-destructive inspection method according to claim 9,wherein the weld inspection fluoroscopic image, in which densityirregularities are corrected, is displayed on the display screen,together with the weld inspection fluoroscopic image in which densityirregularities are not corrected.
 12. The non-destructive inspectionmethod according to claim 10, wherein the weld inspection fluoroscopicimage, in which density irregularities are corrected, is displayed onthe display screen, together with the weld inspection fluoroscopic imagein which density irregularities are not corrected.
 13. A fluoroscopicimage density correction method comprising: acquiring a first inspectionfluoroscopic image generated from a radiation detection medium, which isdisposed to face a radiation source with a welded portion of aninspection target pipe interposed therebetween, at a first inspection;generating a first inspection density profile, which indicates arelationship between density values and coordinates of the firstinspection fluoroscopic image, on the basis of the first inspectionfluoroscopic image; acquiring a second inspection fluoroscopic imagegenerated from a radiation detection medium, which is disposed to face aradiation source with the welded portion of the inspection target pipeinterposed therebetween, at a second inspection; generating a secondinspection density profile, which indicates a relationship betweendensity values and coordinates of the second inspection fluoroscopicimage, on the basis of the second inspection fluoroscopic image;calculating inspection density correction information for matchingrelationships between the density values and the coordinates of thefirst inspection fluoroscopic image and the second inspectionfluoroscopic image, on the basis of the first inspection density profileand the second inspection density profile; and performing densitycorrection for matching relationships between the density values and thecoordinates of the first inspection fluoroscopic image and the secondinspection fluoroscopic image, on the basis of the inspection densitycorrection information.
 14. The fluoroscopic image density correctionmethod according to claim 13, wherein in the generating of the firstinspection density profile, the first inspection density profile isgenerated by performing curve approximation on change in the densityvalue of the first inspection fluoroscopic image in a directionintersecting with the pipe, and wherein in the generating of the secondinspection density profile, the second inspection density profile isgenerated by performing curve approximation on change in the densityvalue of the second inspection fluoroscopic image in a directionintersecting with the pipe.
 15. A non-destructive inspection method,wherein the second inspection fluoroscopic image, in which density iscorrected by the fluoroscopic image density correction method accordingto claim 13, is displayed on a display screen, together with the firstinspection fluoroscopic image in which density is corrected.
 16. Anon-destructive inspection method, wherein the second inspectionfluoroscopic image, in which density is corrected by the fluoroscopicimage density correction method according to claim 14, is displayed on adisplay screen, together with the first inspection fluoroscopic image inwhich density is corrected.
 17. A non-destructive inspection methodcomprising: acquiring a first inspection fluoroscopic image generatedfrom a radiation detection medium, which is disposed to face a radiationsource with a welded portion of an inspection target pipe interposedtherebetween, at a first inspection; generating a first inspectiondensity profile, which indicates a relationship between density valuesand coordinates of the first inspection fluoroscopic image, on the basisof the first inspection fluoroscopic image; acquiring a secondinspection fluoroscopic image generated from a radiation detectionmedium, which is disposed to face a radiation source with the weldedportion of the inspection target pipe interposed therebetween, at asecond inspection; generating a second inspection density profile, whichindicates a relationship between density values and coordinates of thesecond inspection fluoroscopic image, on the basis of the secondinspection fluoroscopic image; calculating inspection density correctioninformation for matching relationships between the density values andthe coordinates of the first inspection fluoroscopic image and thesecond inspection fluoroscopic image, on the basis of the firstinspection density profile and the second inspection density profile;performing density correction for matching relationships between thedensity values and the coordinates of the first inspection fluoroscopicimage and the second inspection fluoroscopic image, on the basis of theinspection density correction information; and displaying the firstinspection fluoroscopic image and the second inspection fluoroscopicimage, in which density is corrected, on a display screen in a reducedmanner on the basis of the diameter of the inspection target pipecalculated in the fluoroscopic image density correction method accordingto claim
 7. 18. The non-destructive inspection method according to claim15, wherein the second inspection fluoroscopic image, in which densityis corrected, is displayed on the display screen, together with thesecond inspection fluoroscopic image in which density is not corrected.19. An image processing device comprising: a fluoroscopic imageacquisition unit that acquires a reference fluoroscopic image generatedfrom a flexible radiation detection medium, which is disposed on anouter circumference of a reference pipe having a reference weldedportion, in case where a radiation source is disposed on a central axisof the reference pipe and radiation originating from the radiationsource is detected by the radiation detection medium, and a weldinspection fluoroscopic image generated from a flexible radiationdetection medium, which is disposed on an outer circumference of aninspection target pipe, in case where a radiation source is disposedinside an inspection target pipe having an inspection target weldedportion and radiation originating from the radiation source is detectedby the radiation detection medium at the time of weld inspection; adensity profile generation unit that generates a reference densityprofile, which indicates a relationship between density values andcoordinates on the reference fluoroscopic image in a direction along theouter circumference of the reference pipe, on the basis of the referencefluoroscopic image, and generating a weld inspection density profile,which indicates a relationship between density values and coordinates onthe weld inspection fluoroscopic image in a direction along the outercircumference of the inspection target pipe, on the basis of the weldinspection fluoroscopic image; a density correction informationcalculation unit that calculates weld inspection density correctioninformation for correcting density irregularities in the weld inspectionfluoroscopic image in the direction along the outer circumference of theinspection target pipe, on the basis of the reference density profileand the weld inspection density profile; and a density correction unitthat corrects the density irregularities in the weld inspectionfluoroscopic image in the direction along the outer circumference of theinspection target pipe, on the basis of the weld inspection densitycorrection information.
 20. An image processing device comprising: afluoroscopic image acquisition unit that acquires an inspectionfluoroscopic image generated from a radiation detection medium which isdisposed to face a radiation source with a welded portion of aninspection target pipe interposed therebetween; a density profilegeneration unit that generates an inspection density profile, whichindicates a relationship between density values and coordinates of theinspection fluoroscopic image, on the basis of the inspectionfluoroscopic image; a density correction information calculation unitthat calculates inspection density correction information for matchingrelationships between the density values and the coordinates of theinspection fluoroscopic image obtained at a previous inspection and theinspection fluoroscopic image obtained at a current inspection, on thebasis of a first inspection density profile generated from theinspection fluoroscopic image obtained at the previous inspection and asecond inspection density profile generated from the inspectionfluoroscopic image obtained at the current inspection; and a densitycorrection unit that performs density correction for matchingrelationships between the density values and the coordinates of theinspection fluoroscopic image obtained at the previous inspection andthe inspection fluoroscopic image obtained at the current inspection, onthe basis of the inspection density correction information.